To achieve higher efficiency and output, some internal combustion engines use turbochargers to pressurize intake air. A turbocharger typically includes a compressor and a turbine, which are mechanically mounted onto a common shaft. The turbine extracts power from the heat and volumetric flow of the exhaust gas exiting the engine and the compressor applies the power to compress the intake air going into the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes the turbine to spin. Since the compressor and the turbine are linked by the common shaft, the rotary action of the turbine causes the compressor to spin and pressurize the intake air to the engine.
Controlling the flow of exhaust gas to the turbine can improve the efficiency and the operational range of a turbocharger. To control the exhaust gas flow, the turbocharger may use a variable exhaust nozzle. One type of variable exhaust nozzle involves the use of multiple, pivoting nozzle vanes located annularly around the inlet to a turbine.
The turbocharger can control the positions of the pivoting nozzle vanes to alter the throat area of the passages between the nozzle vanes. By altering the throat area, the turbocharger can control the exhaust gas flow into the turbine. Typically, the turbocharger controls the positions of the pivoting nozzle vanes by rotating a unison ring that is mechanically connected to each of the nozzle vanes. The unison ring is typically located inside the turbine housing with the nozzle vanes, the turbine and other components.
The components inside the turbine housing may be manufactured with surfaces and cavities that can be pressurized by the exhaust gas to different air pressures. These differential gas pressures inside the turbine housing often lead to axial loading on the components. Excessive axial loading can cause increased friction between the components, which will lead to increased actuation response time and premature failure due to excessive wear.
Thus, there is a need to effectively manage axial loading on components inside the turbine housing in a turbocharger.